Process and apparatus for digesting fibrous material



Jan. 16, 1934. Q Q SCHOENWERK 1,943,489

PROCESS AND APPARATUS FOR DIGESTING FIBROUS MATERIAL Filed May 4, 1932 STORAGE 5 k Y S 0 u w E V) [U 9 Q grwcm bo'v 0. C. Scfioenwen Patented Jan. 16, 1934 UNITED STATES PROCESS AND APPARATUS FOR DIGESTING FIBROUS MATERIAL Otto C. Schoenwerk, Chicago, Ill., assignorto Chemipulp Process, Inc., Watertown, N. Y., a corporation of New York Application May 4, 1932. Serial No. 609,299

27 Claims.

This invention relates to improvements in digesting systems, and more particularly to a novel system of the type in which hot gases, vapors and liquors, vented from digesters during the .cooking of fibrous material, are employed to heat cooking liquor in an accumulator, from which hot preconditioned cooking liquor is-taken for use in a subsequent cook.

, Heretofore, it has been proposed, after a digester is charged with wood chips or the like, to

pump hot cooking liquor from an accumulator into the digester while venting air from the digester to the atmosphere. When acid gas commences to escape, the air vent is closed and the acid gas is diverted to a cooking liquor storage tank. Afterwards, as soon as the digester is completely filled by the liquor, the operation of the pump is continued to pump a relatively high pressure on the substances within the digester. Then the digester is sealed and left under pressure for a time sufficient to permit the liquor to penetrate the fibrous material undergoing treatment. Subsequent to this period, steam is turned into the digester, and during the cooking operation, venting of gases and vapors takes place through the top of the digester, and venting of liquor takes place through'the side'of the digester. These relief fluids, during the cooking operation, are fed into the accumulator for the purpose of absorbing acid gas and preheating and preconditioning the cooking liquor in the accumulator.

The primary purpose of this invention-is to improve systems of that type so as to produce the same quality pulp in a shorter cooking time; toeconomize on the amount of equipment required; to maintain a higher temperature in the accumulator, and to permit better control over the acid strength and temperature in the abcumu- With the foregoing objects outlined and with other objects in view which will appear as the description proceeds, the invention consists in the novel features hereinafter described in detail,

sary in working in accordance with my invention.

' illustrated the accompanying drawing, and

more particularly pointed out in the appended claims.

The drawingshows an end elevation of my improved apparatus used in practicing the process.

Referring to the drawing, 1 designates a digester, and 2 an accumulator. ,It will be under stood that I contemplate using either one or more digesters in combination with the single accumulator 2.

3, 4, 5 and 6 designate respectively, headers which run parallel to the digesters, the header 3 being the cold gas vent, the header 4 the hot gas and vapor vent, 5 the side liquor vent, and'6 the header for feeding the preconditioned and pre-- heated cooking liquor from the accumulator. to the digester. I

A gas or vapor vent branch 7, having a control valve 8 leads from the top of each digester to a cross 9, and the upper branch of the cross is connected by a pipe 10 having a valve 11, to

the cold gas header 3. A conduit 12 having a valve 13, connects one arm of each cross to the hot gas and'vapor header 4. A side relief branch 14 having a valve 15 connects each digester to the header 5, and at the point where the branch 14 connects with the header 5, an upstanding pipe 16 having a valve-17, connects the header 5 to the downwardly extending arm of the cross 9. A single conduit 18 arranged at the same elevation as the vent pipes '7 of the digesters, connects the header 4 with the gas or vapor inlet of an upper eductor 19. The outlet of this eductor is directed downwardly and is connected to a down pipe 20 which leads to the inlet of a lower eductor 21 that is connected by a pipe 22 to the accumulator.

The side relief header 5 is also connected to the inlet of the last mentioned eductor by the following means. A down pipe 23 having a check valve 24 is connected to a T 25, the upper branch of which is connected to a pipe 26 having a con trol valve-2'7. Pipe 26 leads to .the suction of a continuously operated pump 28, the discharge of which is connected by a pipe 29 to the inlet of the lower eductor 21.

Inorder that liquor may be circulated through the accumulator and the eductor 21 by means of the pump .28, a pipe 30 having a valve 31, leads to a second T 32 that is connected with the T 25.

, Hot preconditioned liquor from pipe 30 can be fed to the header 6 by means of a pump 33, the suction of which is connected by a pipe 34 to the T 32, and the discharge of which is connected by a pipe 35 to the header 6.

Hot liquor from the last mentioned header may 1 0 branch pipes 36 that join the header to the digesters. Each of these branches has a control valve 37 and a check valve 38.

Liquor from an acid storage tank 39 isforced from the same by a pump 40, the suction of which is joined to the storage tank by a pipe 41 having a control valve 42. An upstanding pipe 43 joins the discharge of the pump to a check valve 44 leading into the inlet end of the upper eductor 19.

The cold air or gas header 3, has a valve 45 which permits this header to discharge to atmosphere during the filling of a digester, but as soon as acid gas appears in the header, it can be diverted by a pipe 46 which leads from the header 3 into the storage tank 39.

Any excess gas accumulating in the accumulator can be led to the storage tank by means of a pipe 47 having a control valve 48.

Each digester has a gauge glass 49, and the accumulator also has a gauge glass 50.

It will be noted that by using two eductors, thatis, the one 19 at the top, and the one 21 at the bottom of the drop leg 20, and by br;nging the side relief liquor into the suction side of the lower eductor pump 28, only one main relief header is required, that is, the header 4. The header 3 is installed in accordance with prior practice, with the valve 45 opening into.

the digester room. The second header 5 is provided to take care of the side relief separately from the top or gas relief.

As an illustration of the use of my new method, the digester is filled in the usual way, and then the cover is bolted 'on, and the valve 31 at the bottom of the accumulator is opened. The pump 33 is then started, and liquor is pumped into the digester until the same is completely filled with chips or the like and liquor. During this time, of course, valves 8, 11 and 45 are opened, and valves 13, 17 and 15 are closed. As soon as acid gas appears at the valve 45, that valve is closed, and the gas which arises from the liquor during the filling is then vented through the pipe 46 into the acid storage tank. As soon as the digester is completely filled by the liquor which is always evident by the change in sound of the liquor, flowing through valve 8, that valve is closed and a pressure of about 50 pounds is pumped on the digester. The digester is then allowed to stand for a short while to allow a proper absorption of the hot liquor by the chips, and then steam is turned-into the digester in the usual way. Normally, the digester is allowed to stand for about thirty minutes. All of such operation is in accordance with the work of prior inventors.

As soon as steam has been turned on and the pressure has been brought up to the proper fore, that the pumped liquor will set up suction in the pipe 18, and that the heat of the vent gases will be imparted to the liquor in the eductor 19, and at the same time gas will be absorbed therein by the liquor'..

' be introduced into any one of the digesters by The pump 28 runs all the time, as the function of the lower eductor is to put a suction on the line 20, thereby assisting the eductor 19 in keeping the pressure down in the header 4. In other words, the lower eductor 21 places a suction on the drop leg 20 which keeps the liquor level in the drop leg 20 at a low elevation, thereby preventing a back pressure on the eductor 19.

When the temperature and pressure in the digester have reached the proper points for side relief to start, the valve 8 is closed and the valve 15 is opened, so that the side relief liquor is vented through the pipe 14, valve 15, header 5, down pipe 23 check valve 24 and pipe 26, into the suction side of the pump 28. Pump 28 will, of course, be running at this time, and it is taking its supply of liquor from the bottom of the accumulator through the valve 31, the suction line 30, and the suction line 26. When the side relief, however, begins to vent through the connections above mentioned, and arrives at the suction side of the pump, as the pressure in the digester is higher than the pressure in the accumulator, the pump 28 automatically takes a larger proportion of its circulating liquor from the side relief than it does from the accumulator. Consequently, the side relief liquor can be discharged from the digester in a shorter period of time than heretofore, and the whole relieving of this liquor is practically automatic, due to the fact that the pump 28 will take more liquor from the side relief than it does from the bottom of the accumulator.

As soon as the proper amount of side relief liquor has been taken out of the digester, as indicated by the gauge glass 49, the valve 15 is closed, and the valves 8 and 13 are opened while the valves 11 and 17 remain closed. Then the digester is vented through the top in the normal way. Thereafter, the digester vents through the valves 8 and 13 and the branch 12 into the header 4, until the time in the cook when it is necessary to lower the pressure in the digester. This point of time in the cooking, of course, varies with the length of the cook, the strength of the. acid, the moisture content of the wood, and many other factors that have to be determined for each plant, due to the existence of local conditions. However, when this time arrives, the valve 8 is left open, the valve 13 is closed, and the valve 17 is opened. Then the suction of the pump 28 draws 'out what is known as the low pressure relief gases and vapors, through 8, 7, 9, 1'7, 16, 5, 23, 24, 25, 2'1, and 26, and these gases and vapors are mixed with the liquor flowing to the pump 28 from the pipe 30. This feature allows me to considerably shorten the time previously required for blowing down the pressure on the digester, and thereby saves in the cooking time, as the maximum pressure and temperature do not have to be changed in any way. That is, the maximum pressure is maintained for the normal length of time, but the rapid relieving of these blow down gases and vapors at the end of the cook saves considerable time in cooking, as under previous ways of operating, it was found that considerable time was required to take care of the blow down gases and vapors.

It will be noted that I have effected a material and beneficial change by carrying the side relief liquor separately into the suction of the lower ejector pump, and also by causing this pump to take care of the blow down gases and vapors, I shorten the cooking time, and reduce the amount of equipment required. Usually, the

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low pressure gases and vapors were sent to the storage tanks where a proportion of the heat is dissipated, due to the fact that such tank is normally located outdoors. In my improved method, these gases and vapors are conducted to the accumulator, and therefore, the temperature of the liquor in the latter may be maintained at a higher degree, and furthermore, this enables one to have better control over the acid strength and temperature in the accumulator.

Also, in accordance with my invention,with-' out employing any special complicated regulating devices, I can maintain a very low pressure in the relief header 4, which means again that the blow down period during which the gases have to vent through the header 5 is materially reduced.

Furthermore it will be noted that in an apparatus according to the invention, the gas and vapor inlet pipe 18 of the upper eductor 19 can be located on the same level as thebranches 7 of the digestors, and this makes the apparatus function more smoothly. The arrangement is such that one can maintain a very low pressure in the line 4 even with a great number of digesters in a plant. The arrangement has worked successfully in a plant where six .digesters were used in connection with a single accumulator.

In actual practice, the pump 28 would normally be located on approximately the same level as the pump 33 in order to keep the suctionlift as low as possible.

From the foregoing it is believed that the con struction of the apparatus and steps of the method may be clearly understood by those skilled in the art, and I am aware that changes may be made in the details of the apparatus and in the sequence of steps of the method, without departing from the spirit of the invention, as expressed in the claims. I

What is claimed and desired to be secured by Letters Patent is:

1. In the chemical cooking of fibrous material, venting a relief fluid from a digester during the cooking period, circulating an acid liquor by pumping the same in an annular path, and introducing said relief fluid into the circulating liquor at the suction side of the pump.

- 2. In the chemical cooking of fibrous material, venting gases and vapors from a digester during the cooking period, circulating acid liquor in an armular path by a pumping operation, and introducing said relief gases and vapors into the circulating stream of acid liquor at the suction side of the pump;

3: In the chemical cooking of fibrous material, venting side relief liquor from a digester during the cooking period, circulating acid liquor in an annular path by a pumping operation, and introducing said side relief liquor into the circulating stream of acid liquor at the suction side of the pump. a

4. In the chemical cooking of fibrous material, pumping a stream of acid liquor, and utilizing the force of the moving stream for lowering the pressure in the digester during the blow down period of the cooking operation.

5.'In the chemical cooking of fibrous material, pumping a stream of acid liquor, and utilizing the force of the moving stream for lowering the pressure in the digester during the blow down period of the cooking operation by withdrawing gases and vapors from the top of the digester during the blow down period and introducing the same into the stream at the suction side of the pump.

. 6. In the chemical cooking of fibrous material, pumping an endless stream of acid liquor through an accumulator, and utilizing the suction exerted by the pump for withdrawing gases and vapors from a digester during the blow down period of the cooking operation, and for introducing said gases and vapors into said stream, whereby the lowering of the pressure in the digester is accelerated during the blow down period.

7. In a process of the character described, forcing acid liquor from a storage tank through first and second eductors arranged in series, into an accumulator, simultaneously circulating a stream of acid liquor by pumping the same through the second eductor and accumulator,

utilizing the suction of the first eductor for withdrawing relief fluid from a digester, and

utilizing the suction of the pump also for withdrawing relief fluid from the digester.

8. Ina process of the character described, forcing acid liquor from a storage tank through first and second eductors arranged in series, into an accumulator, simultaneously circulating a stream of acid liquor by pumping the same through the second eductor and accumulator; utilizing the suction of the first eductor for withdrawing relief fluid from a digester utilizing the suction of the pump also for withdrawing relief fluid from the digester, and mixing the first mentioned relief fluid with acid liquor in the first eductor.

9. In a, process of the character described,

forcing acid liquor from a storage tank through first and second eductors arranged in series, into an accumulator, simultaneously circulating a stream of acid liquorby pumping the same through the second eductor and accumulator,.

utilizing the suction of the first eductor for withdrawing relief fluid from a digester, utilizing the suction of the pump. also for withdrawing relief fluid from the digester, and mixing the second mentioned relief fluid with the circulating liquor.

10. In a process of the character described, forcing acid liquor from a storage tank through first and second eductors arranged in series, into an accumulator, simultaneously circulating a stream of acid liquor by pumping the same through the second eductor and accumulator, utilizing the suction of the first eductor for withdrawing relief fluid from a digester, utilizing the suction of the pump also for withdrawing relief fluid from the digester, and simultaneously mixing the first mentioned relief fluid with acid a liquor in the first eductor, and the second mentioned relief fluid with-the circulating'liquor at v the suction side of the pump.

v 11. In a process of the character described, discharging relief fluid from the top of a digester through a horizontally disposed passageway, introducing said fluid in the same horizontal plane into the gas inlet of an eductor, and si-' multaneously forcing acid liquor through said eductor for maintaining a substantially constant pressure in said passageway. I I

12. In a process of the character described, si-

multaneously discharging relief gases and vapors anterior to the second pump.

simultaneously forcing acid liquor through the eductor for maintaining a substantially constant pressure in said passageway and its branches.

13. An apparatus for the chemical cooking of fibrous material, comprising a pressure accumulator, a pipe leading from the accumulator back to theaccumulator, a pump interposed in said pipe, a digester, and a relief conduit for the digester leading from the latter to the pipe anterior to said pump.

' 14. An apparatus for the chemical cooking of fibrous material, comprising an accumulator, a pipe leading from the accumulator back to the accumulator, a pump interposed in said pipe, a digester, a relief conduit for the digester leading from the latter to the pipe anterior to said pump, and a side relief header interposed in said conduit.

15. An apparatus for the chemical cooking of fibrous material, comprising a pressure accumulator, a pipe leading from the accumulator backto the accumulator, a pump interposed in said pipe, a digester, a relief conduit for the digester leading from the latter to the pipe anterior to said pump, a side relief header interposed in said conduit, and a valve in the conduit between the digester and said header.

16. An apparatus for the chemical cooking of fibrous material, comprising an accumulator, a pipe leading from the accumulator back to the accumulator, a pump interposed in said pipe, a digester, a relief conduit for the digester leading from the latter to the pipe anterior to said pump, a side relief header interposed in said conduit, and a check valve in the conduit between said header and said pipe.

- lator, a pipe leading from the accumulator back to the accumulator, a pump interposed in said pipe, a digester, a relief conduit for the digester leading from the latter to the pipe anterior' to said pump, and an eductor in said pipe posterior tosaid pump. r

18. An apparatus of the character described, comprising a digester, an accumulator, astorage tank, a first eductor, a first pipe connecting the storage tank to the first eductor, a pump interposed iri said pipe for forcing liquorfrom the storage tank to said eductor, a second pipe connecting the outlet of the eductor to the accumulator, a second eductor interposedin the second pipe, a third pipe connecting the accumulator to the inlet of the second eductor, a second pump interposed in the third pipe, a first valved conduit connecting the top of the digester to the first eductor, and a second valved conduit connecting the first conduit to said third pipe 19. An apparatus of the character described, comprising a digester, an accumulator, a storage tank, a first eductor, a first pipe connecting the storage tank to the first eductor, a pump interposed in said pipe for forcing liquor from the.

storage tank to said eductor, a second pipe con necting the outlet of the eductor to the accumulator, a second eductor interposed in the second pipe, a third pipe connecting the accumulator to the inlet of the second eductorya second pump interposed in the third pipe, a first valved conduit connecting the top of the digester to the first eductor, a-second valved conduit connecting the first conduit to said third pipe anterior to the second pump, and a gas and vapor header interposed in the first conduit.

20. An apparatus of the character described, comprising a digester, an accumulator, a storage tank, a first eductor, a first pipe connecting the storage tank to the first eductor, a pump interposed in said pipe for forcing liquor from the storage tank to said eductor, a second pipe connecting the outlet of the eductor to the accumulator, a second eductor interposed in the second pipe, a third pipe connecting the accumulator to .the inlet of the second eductor, a second pump interposed in the third pipe, a first valved conduit connecting the top of the digester to the first eductor, a second valved conduit connecting the first conduit to said third pipe anterior to the second pump, and a side relief header interposed in the second conduit.

21. An apparatus of the character described, comprising a digester, an accumulator, a storage tank, a first eductor, a first pipe connecting the storage tank to the first eductor, a pump interposed in said pipe for forcing liquor from the storage tank to said eductor, a second pipe connecting the outlet of the eductor to the accumulator, a second eductor interposed in the second pipe, a third pipe connecting the accumulator to the inlet of the second eductor, a second pump I interposed in the third pipe, at first valved conduit connecting the top of the digester to the first eductor, a second valved conduit connecting the first conduit to said third pipe anterior to the second pump, a side relief header interposed in the second conduit, and a valved side relief branch connecting said digester to said header.

22. An apparatus of the character described, comprising a digester, an accumulator, a storage tank, a first eductor, a first pipe connecting the storage tank to the first eductor, a pump interposed in said pipe for forcing liquor from the storage tank to said eductor, a second pipe connecting the outlet of the eductor to the accumulator, a second eductor interposed in the second pipe, a third pipe connecting the accumulator to the inlet of the second eductor, a second pump interposed in the third pipe, a first valved conduit connecting the top of the digester to the first eductor, and a second valved conduit connecting the first conduit to said third pipe anterior to the second pump, said first conduit having two valves and a gas and vapor header interposed between the digester and the first eductor...

23. An apparatus of the character described, comprising a digester, an accumulator, a storage tank, a first eductor, a first pipe connecting the storage tank to the first eductor, apump interposed in said pipe for forcing liquor from the storage tank to said eductor, a second pipe connecting the outlet of the eductor to the accumulator, a second eductor interposed in the second pipe, a third pipe connecting the accumulator to the inlet of the second eductor, a second pump interposed in the third pipe, a first valved conduit connecting the top of the digester to the:

first eductor, a second valved conduit connecting the first conduit to said third pipe anterior to i the second pump, a side relief header interposed in the second conduit, and a valve in the secondconduit between the first conduit and said header. 24. An apparatus of the character described,

comprising a digester, an accumulator, a storage cumulator, a'second eductor interposed in the second pipe, a third pipe connecting the accumulator to the inlet of the second eductor, a second pump interposed in the third pipe, a first valved conduit connecting the top of the digester to the first eductor, a second valved conduit con-* necting the first conduit to said third pipe .an-

terior to the second pump, a forth pipe connecting the third pipe to the bottom of the digester, and a pump interposed in the fourth pipe for forcing acid liquor from the accumulator into terposed in said pipe for forcing liquor from the storage tank to said eduetor,. a second pipe connecting the outlet of the eductor to the accumulater, a second eductor interposed in the second pipe, a third pipe connecting the accumulator to the inlet of the second eductor, a second pump interposed in the third pipe, a first valved conduit connecting the top of the digester to the first eductor, a second valved conduit connecting the first conduit to said third pipe anterior to the second pump, and a third valved conduit con-' necting the first conduit to the storage tank.

26. -An apparatus of the character described, comprising a digester, an accumulator, a storage tank, a first eductor, a first pipe connecting ,the storage tank to the first eductor, a pump interposed in said pipe for forcing liquor from the storage tank to said eductor, a second pipe connecting the outlet of the eductor to the accumulator, a second eductor interposed in the second pipe, a third pipe connecting the accumulator to the inlet of the second eductor, a second pump interposed iii-the third pipe, a first valved conduit connecting the top of the 'digester to the first" eductor, a second valved conduit connecting the first conduit to said third pipe anterior to the second pump, a third valved conduit connecting the first conduit to the storage tank, and an air vent valve interposed in the third conduit.-

27. An apparatus of the character described, comprising a digester, an accumulator, a storage tank, a first eductor, a first pipe connecting the storage tank to the first eductor, a pump interposed in said pipe for forcing liquor from the storage tank to said eductor, a second pipe connecting the outlet of .the eductor to the accumulator, a second eductor interposed in the second pipe; a third pipe connecting the accumulator to the inlet of the second eductor, a second pump interposed in the third pipe, a first valved conduit connecting the top of the digester to the first eductor, a second valved conduit connecting the first conduit to said third pipe anterior to the second pump, and a valved passageway placing the top of the accumulator in communication with the storage tank.

OTTO ,C. SCHOENWERK. 

